The present invention relates to an apparatus for the accurate positioning of assays with respect to reading apparatuses. More specifically, the present invention relates to a carousel on which a plurality of disposable cartridges containing solid-phase assays are expediently positioned with minimal effort to a high degree of accuracy with respect to an optical reading apparatus through a series of locating nubs and tabs.
Solid-phase procedures and apparatuses for performing immunoassays in general and enzyme immunoassays in particular are generally well known in the art. These immunoassays can be performed on biological samples such as blood, spinal fluid, urine, serum, and plasma, to name a few. One particularly cost effective apparatus which has been developed and adapted for use in conjunction with solid-phase procedures to perform a variety of assays (such as sandwich and competitive assays) is a disposable assay cartridge having a plurality of wells, with at least one reaction well. The reaction well generally contains a fibrous matrix positioned across its entrance and an absorbent material positioned below the fibrous matrix. Microparticles, contained in or introduced into the fibrous matrix, react with a sample and an analyte-containing reagent which have been added to the reaction well to form an immobilized complex on the matrix. The excess sample and reagent are washed through the matrix and captured in the absorbent material below.
The resulting assay may be read using known optical detection apparatuses. For example, using conventional solid-phase procedures, the analyte can be labelled or tagged with a fluorophor which, when excited by light of a known wavelength, fluoresces and emits light at a second known wavelength. The intensity of the emitted light is indicative of the concentration of the analyte in the biological sample. A conventional fluorometer is suitable for illuminating the fibrous matrix with a beam of light having the appropriate excitation wavelength. The fluorometer also detects the intensity of the light at the emission wavelength. Assays using this type of solid-phase technology have been found to provide a high degree of sensitivity.
Disposable assay cartridges such as those described above are particularly well suited for use in automated assay preparation and reading equipment. Due to the high degree of sensitivity of assays using the fibrous matrix technology, it is imperative in such automated equipment that the assay-containing reaction well of each and every cartridge be positioned with a high degree of accuracy in each of three dimensions with respect to the optical reading apparatus in order to ensure that the readings have a repeatable high degree of accuracy.
The assays must not only be precisely positioned, they must be effortlessly and transparently positioned by even an unskilled operator with the same high degree of accuracy, in order to reduce the time and cost of each assay. That is, when the assays can be performed and read in a mass production-type manner, the unit cost for such assays decreases. In addition, the assay results can be made available more quickly.
A variety of automated assay equipment is known in the art. Such equipment typically includes apparatuses for moving various types of assay containers between certain assay preparation stations These known apparatuses also position the prepared assays in proximity to various optical equipment for reading. However, known moving apparatuses employed in such equipment are not suitable for use with disposable cartridge type assay containers of the previously described type. In addition, although some such apparatuses have in the past included locking means for retaining individual assay containers, such apparatuses have lacked means to provide the precise assay positioning necessary to obtain highly accurate and repeatable optical readings.
For instance, in some known equipment the assays are placed in individual cuvettes or test tubes in a linear arrangement for movement in conveyor belt fashion past various preparation stations and ultimately to a reading station. Yet, these conveyor belts are difficult to accurately position, both in the path of movement as well as perpendicular to that path. In addition, when arranged in this fashion, the assays are sometimes jostled, thus producing elevational variations which result in inaccurate readings.
Additionally, assays have been arranged in individual cuvettes or test tubes on a rotatable carousel rack. The carousel is circularly indexed to sequentially position the assays at various preparation stations and ultimately at a reading station containing an optical reading apparatus, such as a fluorometer. In this instance, the carousel has three potential positioning inaccuracies. The cuvette may be improperly positioned (1) radially with respect to the center of the carousel, (2) vertically with respect to the optical axis, and (3) laterally with respect to the radial axis in which the cuvette is held in the carousel In addition, all of the previously used apparatuses have failed to provide means for effortlessly and transparently loading, locking, and precisely positioning a plurality of test tubes, cuvettes or other assay containers on the carousel, as well as for releasing such containers after the assays have been read.